970 research outputs found
Direct Observation of a One Dimensional Static Spin Modulation in Insulating La1.95Sr0.05CuO4
We report the results of an extensive elastic neutron scattering study of the
incommensurate (IC) static spin correlations in La1.95Sr0.05CuO4 which is an
insulating spin glass at low temperatures. The present neutron scattering
experiments on the same x=0.05 crystal employ a narrower instrumental
Q-resolution and thereby have revealed that the crystal has only two
orthorhombic twins at low temperatures with relative populations of 2:1. We
find that, in a single twin, only two satellites are observed at (1, +/-0.064,
L)(ortho) and (0, 1+/-0.064, L)(ortho), that is, the modulation vector is only
along the orthorhombic b*-axis. This demonstrates unambiguously that
La1.95Sr0.05CuO4 has a one-dimensional static diagonal spin modulation at low
temperatures, consistent with certain stripe models. We have also reexamined
the x=0.04 crystal that previously was reported to show a single commensurate
peak. By mounting the sample in the (H, K, 0) zone, we have discovered that the
x=0.04 sample in fact has the same IC structure as the sample. The
incommensurability parameter d for x=0.04 and 0.05, where d is the distance
from (1/2, 1/2) in tetragonal reciprocal lattice units, follows the linear
relation d=x. These results demonstrate that the insulator to superconductor
transition in the under doped regime (0.05 </= x </= 0.06) in La2-xSrxCuO4 is
coincident with a transition from diagonal to collinear static stripes at low
temperatures thereby evincing the intimate coupling between the one dimensional
spin density modulation and the superconductivity.Comment: 9 pages 8 figure
Factors associated with the utilization of community dental services among newly incarcerated adults
Background: Given the high rates of risky behaviors and health conditions among incarcerated individuals and the relationship between oral and general health, receipt of quality dental care is essential to the overall health and well-being of this population. However, few recent studies have focused on access to care and the state of oral health among incarcerated populations in the U.S. For the current study, a secondary data analysis was conducted to: 1) assess factors associated with the use of dental services among a newly incarcerated prison population in Georgia and 2) consider barriers related to utilization of dental services pre- to post-release.
Methods: Descriptive statistics were calculated, and bivariate and logistic regression analyses were conducted utilizing SAS 9.2 software. Results: Thirty-one percent (n=250) of survey respondents reported having a dental visit within the past year. Survey respondents who had a regular dentist (OR: 1.9; 95% CI: 1.325, 2.697), private dental insurance (OR: 1.5; 95% CI: 1.022, 2.245), or who reported pain as the reason for their last dental visit (OR: 2.2; 95% CI: 1.556, 3.130) were more likely to have utilized dental services within the past year.
Conclusions: The findings highlight the role of social and economic resources and oral health needs on utilization of dental services. Additional practice and policy efforts are needed to address gaps in the dental care continuum that affect currently and formerly incarcerated adults in Georgia
Midinfrared Conductivity in Orientationally Disordered Doped Fullerides
The coupling between the intramolecular vibrational modes and the doped
conduction electrons in is studied by a calculation of the
electronic contributions to the phonon self energies. The calculations are
carried out for an orientationally ordered reference solid with symmetry and for a model with quenched orientational disorder on the
fullerene sites. In both cases, the dispersion and symmetry of the renormalized
modes is governed by the electronic contributions. The current current
correlation functions and frequency dependent conductivity through the
midinfrared are calculated for both models. In the disordered structures, the
renormalized modes derived from even parity intramolecular phonons are resonant
with the dipole excited single particle spectrum, and modulate the predicted
midinfrared conductivity. The spectra for this coupled system are calculated
for several recently proposed microscopic models for the electron phonon
coupling, and a comparison is made with recent experimental data which
demonstrate this effect.Comment: 32 pages + 9 postscript figures (on request), REVTeX 3.
Unconventional ferromagnetic and spin-glass states of the reentrant spin glass Fe0.7Al0.3
Spin excitations of single crystal Fe0.7Al0.3 were investigated over a wide
range in energy and reciprocal space with inelastic neutron scattering. In the
ferromagnetic phase, propagating spin wave modes become paramagnon-like
diffusive modes beyond a critical wave vector q0, indicating substantial
disorder in the long-range ordered state. In the spin glass phase, spin
dynamics is strongly q-dependent, suggesting remnant short-range spin
correlations. Quantitative model for S(energy,q) in the ``ferromagnetic'' phase
is determined.Comment: 4 pages, 5 figure
Effect of a magnetic field on long-range magnetic order in stage-4 and stage-6 superconducting La2CuO(4+y)
We have measured the enhancement of the static incommensurate spin-density
wave (SDW) order by an applied magnetic field in stage-4 and stage-6 samples of
superconducting La2CuO(4+y). We show that the stage-6 La2CuO(4+y) (Tc=32 K)
forms static long-range SDW order with the same wave-vector as that in the
previously studied stage-4 material. We have measured the field dependence of
the SDW magnetic Bragg peaks in both stage-4 and stage-6 materials at fields up
to 14.5 T. A recent model of competing SDW order and superconductivity
describes these data well.Comment: Published version. 6 pages. 1 figure adde
Critical dynamics of a spin-5/2 2D isotropic antiferromagnet
We report a neutron scattering study of the dynamic spin correlations in
RbMnF, a two-dimensional spin-5/2 antiferromagnet. By tuning an
external magnetic field to the value for the spin-flop line, we reduce the
effective spin anisotropy to essentially zero, thereby obtaining a nearly ideal
two-dimensional isotropic antiferromagnet. From the shape of the quasielastic
peak as a function of temperature, we demonstrate dynamic scaling for this
system and find a value for the dynamical exponent . We compare these
results to theoretical predictions for the dynamic behavior of the
two-dimensional Heisenberg model, in which deviations from provide a
measure of the corrections to scaling.Comment: 5 pages, 4 figures. Submitted to Physical Review B, Rapid
Communication
Spin correlations in an isotropic spin-5/2 two-dimensional antiferromagnet
We report a neutron scattering study of the spin correlations for the spin
5/2, two-dimensional antiferromagnet Rb_2MnF_4 in an external magnetic field.
Choosing fields near the system's bicritical point, we tune the effective
anisotropy in the spin interaction to zero, constructing an ideal S=5/2
Heisenberg system. The correlation length and structure factor amplitude are
closely described by the semiclassical theory of Cuccoli et al. over a broad
temperature range but show no indication of approaching the low-temperature
renormalized classical regime of the quantum non-linear sigma model.Comment: 4 pages, 3 EPS figure
First-principles study of nucleation, growth, and interface structure of Fe/GaAs
We use density-functional theory to describe the initial stages of Fe film
growth on GaAs(001), focusing on the interplay between chemistry and magnetism
at the interface. Four features appear to be generic: (1) At submonolayer
coverages, a strong chemical interaction between Fe and substrate atoms leads
to substitutional adsorption and intermixing. (2) For films of several
monolayers and more, atomically abrupt interfaces are energetically favored.
(3) For Fe films over a range of thicknesses, both Ga- and As-adlayers
dramatically reduce the formation energies of the films, suggesting a
surfactant-like action. (4) During the first few monolayers of growth, Ga or As
atoms are likely to be liberated from the interface and diffuse to the Fe film
surface. Magnetism plays an important auxiliary role for these processes, even
in the dilute limit of atomic adsorption. Most of the films exhibit
ferromagnetic order even at half-monolayer coverage, while certain
adlayer-capped films show a slight preference for antiferromagnetic order.Comment: 11 two-column pages, 12 figures, to appear in Phys. Rev.
First Principles Calculations of Fe on GaAs (100)
We have calculated from first principles the electronic structure of 0.5
monolayer upto 5 monolayer thick Fe layers on top of a GaAs (100) surface. We
find the Fe magnetic moment to be determined by the Fe-As distance. As
segregates to the top of the Fe film, whereas Ga most likely is found within
the Fe film. Moreover, we find an asymmetric in-plane contraction of our
unit-cell along with an expansion perpendicular to the surface. We predict the
number of Fe 3d-holes to increase with increasing Fe thickness on -doped
GaAs.Comment: 9 pages, 14 figures, submitted to PR
Less than 50% sublattice polarization in an insulating S=3/2 kagome' antiferromagnet at low T
We have found weak long range antiferromagnetic order in the
quasi-two-dimensional insulating oxide which contains
Cr S=3/2 ions on a kagom\'{e} lattice. In a sample with 76%
occupancy of the chromium sites the ordered moment is 1.1(3) per
chromium ion which is only one third of the N\'{e}el value .
The magnetic unit cell equals the chemical unit cell, a situation which is
favored by inter-plane interactions. Gapless quantum spin-fluctuations
(T_NS(Q,\omega)$ in the ordered
phase.Comment: 18 pages, RevTex/Latex, with 6 figure
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